For example, a protective relay apparatus performs an accident determination calculation depending on a size or a phase condition of an input current to an electric power system. When an accident occurs in a protective block, a gate is instructed to remove the block causing the accident, to protect the safe power system. In this protective relay apparatus, a current input converter is provided to convert an external input current into a predetermined analog amount. Through the current input converter, the external input current is taken into a terminal table in the protective relay apparatus by an instrument transformer. The input current is electrically isolated and converted into a predetermined analog amount by an internal transformer. The analog amount is further converted into a digital amount to perform a calculation processing for an accident determination.
Generally, when a current is taken in from an electric power system into a protective relay apparatus, connection from a terminal table as an input unit of the protective relay apparatus to a primary side of a transformer inside the protective relay apparatus is formed by wiring based on direct conduction or by a patterned conductor on a printed circuit board built in the protective relay apparatus.
In this case, there is a need to reduce resistance from the input unit of the protective relay apparatus to a primary side of the transformer inside the protective relay apparatus, in order to ensure an excessive current tolerance for the input unit. Hence, a thick lead such as a copper wire which has a sufficient line diameter is used when wiring is employed. A pattern width is increased when a patterned conductor is used.
Then, when wiring is employed, spaces for terminal connection and for wiring work are required to connect the terminal table as the input unit of the protective relay apparatus and the lead wire inside the protective relay apparatus, and consequently limit the size of the protective relay apparatus. On the other side, when a pattern on the printed circuit board is used for connection from the terminal table as the input unit of the protective relay apparatus to the primary side of the transformer, double-sided patterning is required or a sufficient pattern width is required in order to suppress increase in temperature of a pattern. Upon necessity, consideration is required to increase a pattern film thickness and consequently limits pattern designing and the size of the printed circuit board. In case of wiring a lead, wiring work is required and therefore causes a possibility of a wiring error when the protective relay apparatus is assembled.
In a structure of mounting a transformer aiming at downsizing/thinning and weight reduction, a transformer is inserted into a through hole formed in a printed circuit board, and a secondary coil is wound about a coil bobbin of the transformer. Support legs extending in mutually opposite directions are formed integrally on the coil bobbin. The support legs are bridged over an open end surface of the through hole on a surface side of the printed circuit board. The transformer is configured to suspend from the printed circuit board and is thereby fixed to the printed circuit board (for example, see Jpn. Pat. Appln. KOKAI Publication No. 2004-296471 (hereinafter referred to as “Patent Document 1”)).
In Patent Document 1, however, downsizing/thinning is achieved by modifying the structure of the transformer to simplify assembly of the transformer, and reduction in resistance of a wire or a patterned conductor from a terminal table to a primary side of a transformer inside a protective relay apparatus is not intended. That is, the structure disclosed in Patent Document 1 needs to ensure a sufficient size for the printed circuit board in order to maintain a wiring space or a pattern space on the printed circuit board. Therefore, an input unit of the protective relay apparatus cannot be downsized. In addition, neither wiring work between the terminal table and the primary side of the transformer inside the protective relay apparatus nor wiring check work for preventing wiring errors can be easily carried out.
Under the circumstances, it is desired to provide a current input converter which can shorten connection from a terminal table as an input unit to a primary side of an internal transformer, to satisfy an excessive current tolerance, and can improve work efficiency by preventing wiring errors.